Gas turbines with sequential combustion are known and have been useful in industrial operation.
A gas turbine, known as GT24/26, is disclosed, for example, in an article by Joos, F. et al., “Field Experience of the Sequential Combustion System for the ABB GT24/GT26 Gas Turbine Family”, IGTI/ASME 98-GT-220, 1998 Stockholm. FIG. 1 of this publication is reproduced in the present application as FIG. 1. Furthermore, such a gas turbine is disclosed in EP-B1-0 620 362.
FIG. 1 shows a gas turbine 10 with sequential combustion, in which a compressor 11, a first combustion chamber 14, a high-pressure turbine (HPT) 15, a second combustion chamber 17 and a low-pressure turbine (LPT) 18 are arranged along an axis 19. The compressor 11 and the two turbines 15, 18 are part of a rotor which rotates around the axis 19. The compressor 11 draws in air and compresses it. The compressed air flows into a plenum and from there into premix burners where this air is mixed with at least one fuel which is introduced via the fuel supply 12. Such premix burners are disclosed, for example, in EP-A1-0 321 809 and EP-A2-0 704 657.
The compressed air flows into the premix burners, where the mixing with at least one fuel takes place. This fuel/air mixture then flows into the first combustion chamber 14, in which this mixture can be combusted, forming a stable flame front. The hot gas which is thus made available is partially expanded in the adjoining high-pressure turbine 15, performing work, and then flows into the second combustion chamber 17 where a further supply 16 of fuel can take place. As a result of the high temperatures which the hot gas, which is partially expanded in the high-pressure turbine 15, still has, a combustion, which is based on self-ignition, takes place in the second combustion chamber 17. The hot gas which is reheated in the second combustion chamber 17 is then expanded in a multistage low-pressure turbine 18.
The low-pressure turbine 18 includes a plurality of rows, arranged in series in the flow direction, of rotor blades and stator blades, which can be arranged in alternating sequence. For example, the stator blades of the third stator blade row in the flow direction are provided with the designation 20′ in FIG. 1.
With the high hot-gas temperatures of gas turbines of the latest generation, it is desirable to cool the stator blades and rotor blades of the turbine. For this, a gaseous cooling medium (for example compressed air from the compressor of the gas turbine or steam if the gas turbine is part of a combined cycle power generating plant) can be delivered through cooling passages (frequently extending in a serpentine manner) which can be arranged in the blade, and/or discharged outwards at different points of the blade through corresponding openings (holes, grooves), for example, to form a cooling film on the outer side of the blade (film cooling). An example of such a cooled blade is disclosed in U.S. Pat. No. 5,813,835.
Cooling of the platforms, in particular the outer platform of a gas-turbine stator blade, in which special cooling holes and impingement cooling techniques are used, is known, for example, from printed publication DE-A1-10 2005 013 795. Such cooling devices and cooling techniques, however, require a comparatively high production and installation outlay.